Fix autonomous managed capabilities #733
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Allows
install-capabilityto be called anywhere, by closing the leak exposed by unscoped signatures.install-capabilitysimply mimics the "specify-for-install" part of sig scopes. However, this would be a horrible leak if unscoped signatures could now be in scope for a managed capability installed thus. The fix is to make unscoped signatures unavailable to the environment if any autonomously-installed caps are present.Otherwise, signature scoping prevents install from doing any harm. Autonomous install of a user capability when the associated signature is not scoped to that capability will result in failure to acquire the capability, so this is safe. A user attempting to fool an autonomous authority with a direct call to
install-capabilitywill fail for the same reason such an acquire would fail normally, as the module guard would prevent it.Indeed, autonomous guards are carefully scoped already, and the whole motivation of signature scopes is that signatures were not so scoped. With this change, autonomous caps can return to their inherent security by self-installing the capability before attempting to acquire it, and any other install is harmless by construction. Meanwhile, the one hole left in signature scoping is closed whenever any autonomous install is conducted.